U.S. patent number 6,726,960 [Application Number 08/919,448] was granted by the patent office on 2004-04-27 for protective coating on steel parts.
This patent grant is currently assigned to National Crane Corporation. Invention is credited to Carl Horowitz, Ella Mayslich, Mohan L. Sanduja, Paul Thottathil.
United States Patent |
6,726,960 |
Sanduja , et al. |
April 27, 2004 |
Protective coating on steel parts
Abstract
This invention relates to the coating of steel parts with
organic polymeric materials for resistance to corrosion, abrasion,
impact, salt solutions of high and low pH (both in liquid as well
as vapor state) and corrosive atmospheric gases under the
environment of high relative humidity and ambient conditions of
temperature and pressure. To obtain secure and permanent adhesion
of the coating on the steel article a polymeric coating is
formulated so as to achieve chemical grafting to the steel face.
This involves the use of monomers, prepolymers, catalyst and a
graft initiator system. The monomers are preferably polyfunctional
and when applied onto a metallic substrate, react via graft
polymerization with the metal to form a polymerized layer coated
onto the surface of the steel substrate. The monomers and
prepolymers are so selected that when polymerized onto steel the
coating has substantially zero moisture vapor-gas transmission rate
and consequently acts as a barrier to moisture, oxygen and other
gases from coming in contact with the surface of the steel
substrate thereby improving the protective potential of the
coating. Fillers may be included in the coating material to enhance
physical or wear characteristics. Other components that can be
added are slip agents, wetting agents, thixotropic promoters and
adhesion promoters. This coating process is particularly
advantageous for use with steel parts used in the manufacture of
cranes
Inventors: |
Sanduja; Mohan L. (Flushing,
NY), Horowitz; Carl (Brooklyn, NY), Mayslich; Ella
(Brooklyn, NY), Thottathil; Paul (New Hyde Park, NY) |
Assignee: |
National Crane Corporation
(Waverly, NE)
|
Family
ID: |
23432306 |
Appl.
No.: |
08/919,448 |
Filed: |
August 28, 1997 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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363925 |
Dec 27, 1994 |
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Current U.S.
Class: |
427/388.2;
212/299; 428/461; 427/386; 428/447 |
Current CPC
Class: |
B05D
7/14 (20130101); Y10T 428/31663 (20150401); Y10T
428/31692 (20150401) |
Current International
Class: |
B05D
7/14 (20060101); B66C 032/687 () |
Field of
Search: |
;428/461,447
;212/266,267,299 ;427/388.1,388.2,388.3,388.5,386 |
References Cited
[Referenced By]
U.S. Patent Documents
|
|
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4004695 |
January 1977 |
Hockensmith et al. |
4105811 |
August 1978 |
Horowitz et al. |
4106955 |
August 1978 |
Horowitz et al. |
4453988 |
June 1984 |
Slater et al. |
5015507 |
May 1991 |
DesLauriers et al. |
5043226 |
August 1991 |
Wiedeman et al. |
|
Foreign Patent Documents
Other References
Encyclopeda of Chemical Technology (fourth edition), Vol 6, pp
706-710, 1993..
|
Primary Examiner: Tarazano; D. Lawrence
Attorney, Agent or Firm: Birch, Stewart, Kolasch &
Birch, LLP
Parent Case Text
This application is a continuation of application Ser. No.
08/363,925 filed on Dec. 27, 1994, now abandoned.
Claims
We claim:
1. A process for providing a steel workpiece with a coating of
organic polymeric material, which comprises the steps of: (i)
applying to an exposed face of the workpiece a composition
comprising, (a) a polymerisable material having at least one
constituent selected from each of epoxy prepolymers, and urethane
prepolymers; (b) a monomer or prepolymer having at least one active
group adapted to form graft polymerization linkages with the steel
and with the polymerizable material, selected from the group
consisting of hydroxyl, carbonyl, carboxyl, esters of carboxyl,
amino, and epoxy; (c) a catalytic initiator selected from the group
consisting of ions of iron, silver, cobalt and copper; and (d) a
peroxide selected from the group consisting of benzoyl peroxide,
methyl ethyl ketone peroxide, t-butyl hydroperoxide, and hydrogen
peroxide; and (ii) curing the resulting workpiece.
2. The process claimed in claim 1 wherein the composition further
includes inorganic filler.
3. The process claimed in claim 1 wherein the composition further
includes a slip agent.
4. The process as claimed in claim 3, wherein the slip agent is
selected from the group consisting of molybdenum disulfide,
polytetrafluoroethylene and tungsten disulfide.
5. The process as claimed in claim 1 wherein the composition
further includes wetting agents.
6. The process as claimed in claim 1 wherein the composition
further includes thixotropic agent.
7. The process as claimed in claim 1, wherein the composition
further comprises an adhesion promoter.
8. A coated steel workpiece coated by a process which comprises the
steps of: (i) applying to an exposed face of the workpiece a
composition comprising, (a) a polymerisable material having at
least one constituent selected from each of epoxy prepolymers, and
urethane prepolymers; (b) a monomer or prepolymer having at least
one active group adapted to form graft polymerization linkages with
the steel and with the polymerizable material, selected from the
group consisting of hydroxyl, carboxyl, esters of carboxyl, amino,
and epoxy; (c) a catalytic initiator selected from the group
consisting of ions of iron, silver, cobalt and copper; and (d) a
peroxide selected from the group consisting of benzoyl peroxide,
methyl ethyl ketone peroxide, t-butyl hydroperoxide, and hydrogen
peroxide; and (ii) curing the resulting workpiece.
9. The coated steel workpiece of claim 8, wherein the composition
further comprises (e) an inorganic filler selected from the group
consisting of calcium carbonate, titanium dioxide, mica, magnesium
silicate, alumina, borax, iron oxide and silica.
10. The coated steel workpiece of claim 9, wherein the
polymerizable material (a) includes a vinyl monomer, and the
monomer or prepolymer (b) has a trimethoxysilane group.
11. The coated steel workpiece of claim 8, wherein the
polymerizable material (a) includes a vinyl monomer, and the
monomer or prepolymer (b) has a trimethoxysilane group.
12. A telescopic boom for use in a crane coated with a composition
comprising: (a) a polymerisable material having at least one
constituent selected from each of epoxy prepolymer, and urethane
prepolymers; (b) a monomer or prepolymer having at least one active
group adapted to form graft polymerization linkages with the steel
and with the polymerizable material, selected from the group
consisting of hydroxyl, carbonyl, carboxy, esters of carboxyl,
amino, and epoxy; (c) a catalytic initiator selected from the group
consisting of ions or iron, silver cobalt and copper; (d) a
peroxide selected from the group consisting of benzoyl peroxide,
methyl ethyl ketone peroxide, t-butyl hydroperoxide, and hydrogen
peroxide; and (e) an inorganic filler.
13. A telescopic structure for use in lifting equipment coated with
a composition comprising: (a) a polymerisable material having at
least one constituent selected from each of epoxy prepolymer, and
urethane prepolymers; (b) a monomer or prepolymer having at least
one active group adapted to form graft polymerization linkages with
the steel and with the polymerizable material, selected from the
group consisting of hydroxyl, carbonyl, carboxy, esters of
carboxyl, amino, and epoxy; (c) a catalytic initiator selected from
the group consisting of ions or iron, silver cobalt and copper; (d)
a peroxide selected from the group consisting of benzoyl peroxide,
methyl ethyl ketone peroxide, t-butyl hydroperoxide, and hydrogen
peroxide; and (e) an inorganic filler.
14. A telescopic structure having at least one telescopic section
extendable from and retractable into another telescopic section,
and wear pads subject to high loading forces connected between and
in sliding contact with surfaces of the respective telescopic
sections, and at least the surfaces of the telescopic sections in
sliding contact with the wear pads coated with a composition
comprising: (a) a polymerisable material having at least one
constituent selected from each of epoxy prepolymer, and urethane
prepolymers; (b) a monomer or prepolymer having at least one active
group adapted to form graft polymerization linkages with the steel
and with the polymerizable material, selected from the group
consisting of hydroxyl, carbonyl, carboxy, esters of carboxyl,
amino, and epoxy; (c) a catalytic initiator selected from the group
consisting of ions or iron, silver cobalt and copper; (d) a
peroxide selected from the group consisting of benzoyl peroxide,
methyl ethyl ketone peroxide, t-butyl hydroperoxide, and hydrogen
peroxide; and (e) an inorganic filler.
Description
BACKGROUND OF THE INVENTION
The present invention relates to a protective coating for steel
parts used in the manufacture of cranes. It also relates to a
method of grafting a protective coating onto metallic parts that
not only protects the part from corrosion and other adverse effects
of the environmental conditions of temperature, pressure, humidity,
corrosive gases like hydrogen sulfide, carbon dioxide, sulfur
dioxide but also imparts an excellent degree of abrasion
resistance.
The current process for the production of steel parts used in the
manufacture of cranes doesn't apply organic coatings on the
finished products so as to protect them against corrosion,
abrasion, impact, under environmental conditions of temperature,
pressures, humidity, salt solutions of low and high pH and high
concentration of corrosive gases like hydrogen sulfide, carbon
dioxide, sulfur oxide and other gases. This is particularly true
when the steel cranes are continuously used outdoors in the open
air at ambient conditions of temperature and pressure, where they
are being subjected to wear and tear and more importantly undergo
corrosion. This may be due to the fact that water, water vapor or
moisture readily dissolves a small amount of oxygen from the air in
the solution and this, when condensed on the surface of the steel
substrate, contributes to corrosion. For such a situation, the
present instant invention relates to a process and composition for
graft polymerizing a protective coating onto metallic substrate, so
that the protection is sufficiently durable and is not readily
removed from the metal as it undergoes abrasion and exposure to the
environmental conditions during routine use.
Presently many different types of surface coatings are used in an
effort to achieve the necessary requirements in terms of protection
against corrosion and other properties. These include protective
paints, yellow and clear chromatic coatings, and precious and non
precious metal platings. Each of these methods have coat or
performance deficiencies. Lack of surface resistivity to wear,
abrasion, corrosion, impact, adhesion and durability resistance are
all problems associated with these organic paints and coatings. The
metal platings are generally expensive, and in some cases, are not
tenacious enough for the abrasive environments of corrosion liquids
and gases encountered by these steel products. As these coatings
are applied at a minimal thickness and are physically rather than
chemically bonded to the metallic substrate, they are susceptible
to removal by normal abrasion when used in working conditions in
outdoor environments. These platings are also susceptible to
galvanic corrosion when contacting dissimilar metal surfaces. There
is also a phenomena known as "fretting corrosion" which occurs with
minimal mating pressures and is associated with metal
migration/loss across the boundary area. In these cases, base metal
corrosion occurs and environmental protection is lost. Also, in
some instances, aesthetics are impacted due to surface
contamination and discoloration. Therefore, the tenacity of these
coatings is not sufficient for the requirements as warranted by the
present invention. Even when the metallic parts are coated with
expensive organic coatings, the coatings tend to be permeable to
various corrosive gases and liquids so that the requisite degree of
corrosion protection is not obtained. Because these coatings adhere
to the substrate only through physical bonds, they can be readily
dislodged from the metallic substrate over a short period of time
as moisture, oxygen, chlorine, hydrogen sulfide and other corrosive
gases permeate beneath the coated polymeric film. In view of this,
there is a need for a coating that not only protects the metal from
corrosion but also is abrasion resistant and is tenacious with a
high degree of durability.
U.S. Pat. No. 5,015,507 to Des Lauriero describes a method of
converting a rusted surface to a durable one by using a reducing
agent which will function to reduce trivalent iron to divalent
iron; an organic monomer which is capable of polymerization in the
presence of the reducing agent on the surface; and a free radical
initiator, which will polymerize the organic monomer to form the
durable coating.
U.S. Pat. No. 4,453,988 to Slater discloses a method for coating a
rusted metallic surface that uses a meth(acrylic) monomer; a
peroxide curing system; and drying oil. Both these coating systems
suffer from poor adhesion to the metal surface, since no method is
described for directly bonding the film to the metal.
A number of inventions have been described previous to this instant
invention which address the bonding problem through grafting of the
film. For example, in U.S. Pat. No. 4,105,811 by Horowitz, hereby
incorporated by reference, grafting technology is described to
achieve a transparent, impervious protective coating on aluminum.
In this case a peroxide and silver ion are present to initiate and
catalyze graft polymerization of monomers and prepolymers which
attach to the aluminum surface.
U.S. Pat. No. 5,043,226 to Wiedeman, hereby incorporated by
reference, described a method of grafting a conductive, tenacious
and protective coating on a metallic substrate such as steel,
aluminum iron, platinum or silver. This method employed one or more
polymerizable monomers having at least two functionalities, one or
more graft initiators containing nickel ion and a reducing agent
capable of reducing nickel ion to nickel metal.
U.S. Pat. No. 4,106,955 to Horowitz, hereby incorporated by
reference, relates to the coating of steel articles wherein
monomers containing hydroxyl, carbonyl, amine, glycidyl or
azirdinyl groups react with steel surface to produce a corrosion
and abrasion resistant surface.
The present invention employs a coating composition which differs
from those used previously and provides superior corrosion and
abrasion resistance to those previous compositions now cited. The
instant invention is particularly advantageous for steel cranes
which because of specific metallurgical considerations require a
polymerizable/graftable species and initiator combination which is
adapted to reaction with that specific surface. It is felt that
this process, using the composition specified, will have general
utility in a number of applications. In addition, the superior
bonding achieved will confer improved corrosion and abrasion
resistance in other applications as well.
CHEMICAL GRAFTING--BACKGROUND
Chemical grafting involves the activation of the substrate. Once
the substrate has been activated, chains of monomers linked by
carbon-carbon bonds grow on the substrate as whiskers. These
whiskers impart new and desirable properties permanently imparted
to the substrate without damaging any of the existing positive
characteristics of these materials. Many materials, both naturally
occurring and synthetic, posses hydrogens which are more reactive
than the "bulk hydrogens", for example, the tertiary hydrogen in
polypropylene (1) the amide hydrogen in proteins (2) and the
hydroxyl hydrogen in polysaccharides (3). ##STR1##
Graft initiators (G.I) have the capacity of removing these active
hydrogens and concomitantly initiating the growth of polymer chains
at the side from where the active hydrogen was removed.
In the case of polypropylene, this can be represented as follows:
##STR2##
Where * can represent a free radical, anion or cation, depending on
whether the G.I. removes a hydrogen and one electron, no electrons
or two electrons respectively. (There are a wide variety of
monomers which do not lend themselves to the free-radical type of
polymerization. The use of all three mechanism broadens the scope
of application of this method). ##STR3##
represents a unit of vinyl monomer where "X" governs the property
or properties that are obtained. In many instances a mixture of
monomers is employed and often more than one property can be
altered in one processing step. These polymer chains whose length
can be controlled, are permanently attached to the "substrate". The
linkage between the graft-polymer and the substrate is covalent in
nature, therefore, the graft-polymer cannot be leached from the
substrate. In essence the chemical grafting consisted of growing
polymer chains on the backbone chain of a substrate. The graft
polymer chains are formed from vinyl monomers or monomer containing
appropriate functionability, e.g., groups such as hydroxyl,
carboxyl, epoxy, amide, amine anhydride.
Without being bound by any metal grafting theory, the details of
which have not been fully established, the mechanism of reaction
between the steel surface and monomers or prepolymers is thought to
involve a reactive species on the steel surface. In the presence of
moisture, there is a layer of oxide and hydroxyl groups tenaciously
bound to the steel substrate. The hydrogen of the hydroxyl group
may be removed by the graft initiator and form a radical which
reacts with the monomer starting graft polymerization. The oxides
and hydroxyl groups react with epoxy groups of the prepolymers or
monomers starting a chemical reaction which also leads to a strong
bonding between the steel and organic polymer formed on the
surface.
Thus, the mechanism of graft polymerization may be presented in a
series of steps as follows: ##STR4##
The process of termination may undergo differently when the
formulation contain reactive prepolymers or polymers. The
prepolymers may undergo also activation by the graft initiator
giving reactive radicals P which react with the radical on the
steel surface forming a graft coating on the substrate:
##STR5##
The graft initiator G may consist of the following metal ions;
Fe.sup.+++ /Fe.sup.++, Ag.sup.+, Co.sup.++, Cu.sup.++ and the
peroxide should be chosen from catalysts such as benzoyl peroxide,
methyl ethyl ketone peroxide, tert butyl hydroperoxide and hydrogen
peroxide. The monomers and prepolymers have side functional groups
x, which may react between themselves and with additional
prepolymers or polymers included into the formulation forming a
graft crosslinked organic coating. The functional groups of the
monomers and prepolymers should consist of hydroxyl groups,
carbonyl groups, secondary and/or tertiary amino groups and epoxy
groups. The molecular ratio of the functional groups of the
reactive components should be adjusted so that no free groups
should be left after the reaction is finished.
SUMMARY OF INVENTION
It is accordingly a primary objective of the present invention to
provide an improved process for the graft coating of steel surfaces
with organic polymer material.
Another object of the invention is to provide organic materials
which when coated onto the steel surface effect a graft coating,
bonding the coating to the surface.
Yet another object of the invention is to provide steel workpieces,
and especially crane parts having a coating of organic polymer
material bonded permanently to the steel of the workpiece and
adapted to resist corrosion and have desirable wear resistance and
frictional characteristics.
A Still further object of the invention is to produce coated steel
parts with substantially zero permeability to oxygen and other
corrosive gases and with substantially zero water vapor
transmission rates.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic view of a two-section telescopic boom for a
crane, aerial work platform, or the like, including the coating of
the present invention, the boom being shown in an extended
position;
FIG. 2 is an enlarged cross-sectional view taken substantially
along line 2--2 of FIG. 1; and
FIG. 3 is an enlarged fragmentary, cross-sectional view of the
fragmentary portion labeled FIG. 3 in FIG. 2, and showing the
coating of the present invention on the surfaces of the boom
sections requiring lubrication and which are subject to sliding
friction or abrasive forces.
DESCRIPTION OF THE PREFERRED EMBODIMENT
Many metallic crane parts are subjected to adverse environmental
and operating conditions. These includes salt solutions of high and
low pH (both in liquid as well as vapor state), atmospheric gases
like hydrogen sulfide, carbon dioxide, sulfur dioxide, and others
under a perishable relative humidity >90% and ambient conditions
of temperature and pressure. It has been found that by reactively
coating the unfinished steel of the crane with a polymer which is
chemically bonded to the surface of the steel that the coating is
protective against corrosion and other adverse effects of the
environmental conditions. It also imparts a high degree of abrasion
resistance to the part, especially as used in crane
applications.
Referring to the drawings in greater detail, by way of example of a
structure on which the coating of the present invention has
substantial utility, FIG. 1 shows a two-section telescopic boom 1
for a crane, mobile aerial work platform, or the like. While a
two-section telescopic boom is shown, it is to be understand that
the coating has utility in telescopic booms having three, four, or
more sections, as well as in telescopically extendable and
retractable outriggers, extendable lifting devices in fork lift
trucks, and the like. The telescopic boom includes a base section 2
that is adapted to be pivotally connected at 3 at its innermost end
to a superstructure (not shown), and an outer section 4
telescopically connected in base section 2 and extendable from and
retractable into the base section by a hydraulic cylinder/piston
assembly 5 having one end pivotally connected at 6 adjacent the
innermost end of base section 2, and the outermost end of the
piston rod pivotally connected at 7 adjacent the outermost end of
outer section 4. A hydraulic lift cylinder (not shown) is adapted
to be pivotally connected between the base section at 8 and the
superstructure of the machine, for pivotally raising and lowering
the telescopic boom about boom pivot connection 3, in the
conventional and well known manner.
When the telescopic boom is used in a crane, a boom nose and
lifting assembly is connected to the outermost end 9 of outer
section 4, and when the telescopic boom is used in an aerial work
platform, a work support platform is connected to the outer most
end 9 of the boom.
As shown in FIGS. 2 and 3, the outside surfaces of outer boom
section 4 is coated with the protective coating 10 of the
invention, and the inside surface of boom base section 2 is shown
coated at 10' with the protective coating of the present invention.
These are the surfaces in a telescopic boom that are subject to
sliding friction and abrasion forces, and which normally require
application of lubrication compound. Bottom wear pads 11 are
connected on the front of boom base section 2 in sliding contact
with the bottom surface of outer boom section 4, and top wear pads
12 are connected on the top rear portion of outer boom section 4 in
sliding contact with the top inner surface of boom base section 2.
Front side wear pads 13, connected to the front side walls of boom
base section 2, are in sliding contact with the outer side walls of
outer boom section 4; and rear side wear pads 14, connected to the
rear side walls of outer boom section 4, are in sliding contact
with the inner side walls of boom base section 2. All of the wear
pads 11, 12, 13 and 14 are conventionally constructed of Nylon
material, know commercially as Nylatron. These wear pads may
contain plugs of Teflon inserted therein for additional
lubrication, but are not necessary for the present invention. The
positions of the wear pads shown herein between the telescopic
sections are for example only, and it is to be understood that the
wear pads can be placed in other positions than those shown when
used with the protective coating of the invention.
In the prior art, instead of the protective coating of the present
invention shown at 10 and 10', paint has been used in the past. As
the outermost boom section 4 is extended and retracted relative to
boom base section 2 by the hydraulic cylinder/piston assembly 5,
the wear pads 11, 12, 13 and 14 quickly wear off the prior art
paint coating on the metal surfaces of the boom sections, resulting
in the surfaces of the wear pads being in sliding contact with the
bare metal surface of the respective boom sections. As the prior
art paint coating wears off under the friction force of the wear
pads, the paint coating galls and presents a rough sliding surface
for the wear pads, which causes the outer boom section to chatter
or jump as it is extended and retracted. To combat this, and to
protect the bare metal surfaces of the boom sections against the
elements, that is the metal surfaces left bare due to the paint
coating being worn off, heavy lubricating compounds are applied to
the bare metal surfaces, that is to the tracks on the surfaces
against which the wear pads slide, left bare by the sliding
friction movement therebetween. These lubricating compounds must be
re-applied on a regular basis to prevent corrosion of the boom
sections.
The protective coating of the present invention, shown at 10 and
10', is substituted for the prior art paint coatings, and, as shown
in FIGS. 2 and 3, the surfaces of wear pads 11, 12, 13 and 14 are
in sliding contact with the protective coating on the outside
surface of outer boom section 4 and on the inside surface of boom
base section 2. The protective coating of the present invention,
over extended periods of use, shows no appreciable reduction in
thickness of the coating layer in the area in sliding contact with
the wear pads, does not gall, and provides sufficient lubricity so
as to eliminate the need for application of lubricating compounds
on the boom sections in the slide area of the wear pads, as
required with prior art coatings. This eliminates the maintenance
problem of dirt and contaminant build-up in the applied prior art
lubricating compound, and provides a more aesthetic telescoping
boom structure since the dark streaks of lubricating compound are
eliminated from the boom sections.
While the protective coating of the present invention has been
shown in the drawings at 10 and 10' applied only to the outer
surface of the outermost boom section 4 and the inner surface of
the boom base section 2, in practice the protective coating can
also be applied to both the inner and outer surfaces of all boom
sections, that is even those surface not requiring lubricity, and
not normally subject to sliding frictional forces, because the
anti-corrosive qualities of the protective coating protect all
surfaces of the telescopic boom, as well as the metal surfaces on
other assemblies and portions of the cranes, aerial work platforms,
machines, and the like.
The present invention is based on covering the steel parts with a
protective coating by chemically grafting organic monomers and
prepolymers thereby forming a strongly bonded polymeric film to the
steel surface. The monomers/prepolymers are so selected that the
resulting polymeric film grafted onto the steel parts has
substantially zero permeability to oxygen and other corrosive gases
with substantially zero water vapor transmission rate, which allows
it to improve the protective potential of the substrate. The
polyfunctional monomers/prepolymers are vinyl monomers and epoxy
prepolymers which are believed to be chemically bonded to the metal
substrate via metal oxide. The monomers are preferably acrylic
monomers having one or more hydroxy, carboxy and glycidyl
groups.
Epoxy prepolymers and urethane prepolymers are particularly useful
materials. The above prepolymers can be mixed with another monomer
such as methyl methacrylate along with other ingredients in the
graft polymerization process. Further monomers which can be
included in the above formulations include monomers having
functional groups such as hydroxyl, carboxyl, carbonyl, esters,
amine, amide and glycidyl. The physical and chemical properties of
the prepolymers and monomers included into the formulation have
been chosen so that a high level of protective coating could be
achieved.
Graft initiators like iron, silver, cobalt, copper, cerium, etc can
be used as initiator ions in the graft polymerization process.
However, the use of specific graft initiator ion depends on the
nature of the substrate. In the graft polymerization reaction, the
polymerization composition is comprised of polymerizable
monomerstprepolymers, peroxide type catalyst and graft initiator
system. The peroxide type catalyst is broken into active radicals
by the action of the metallic silver. These radicals in turn
initiate the polymerization of the monomer.
Further the abrasion resistance of the organic polymeric coating
may be increased by incorporating inorganic fillers, such as
calcium carbonate, titanium dioxide, mica, magnesium silicate,
alumina, borax, iron oxide and silica.
In addition, slip agents such as molybdenum disulfide or
fluorinated polymers may be used. Other slip agents that can be
used include Super slip 6530 (a combination of wax polymers having
a melting point of 255-275.degree. F.), tungsten disulfide,
Polymist F5A (micronized polytetrafluoroethylene powder),
Polyfluoro 200 (a combination of polyethylene wax and
polytetrafluoroethylene having a melting point of 255-259.degree.
F.) and Slip Ayd (dispersion of low molecular weight polyethylene
or polymeric wax) Many other conventional additives may be found in
the formulation including pigments, thixotropic promoters,
lubricants slop agents, stabilizers, adhesion promoters, wetting
agents, and anticorrosion agents.
In order to achieve good adhesion between the steel surface and the
coating monomer it is advantageous to add other adhesion promoters.
These can include organo silanes such as amino silanes, epoxy
silanes, and vinyl silanes. Other adhesion promoters include,
Silane A187 (gamma-glycidoxypropyltrimethoxy silane), Silane A110
(gamma-aminopropyltriethoxy silane) acrylate monomers, methacrylate
monomers, titanates and zirconates.
The coating compositions of the present invention further include
thixotropic agents such as, Cab-ol-sil TS720 (hydrophobic fumed
silica), Cab-o-sil TS610 (fumed silica partially treated with
dimethyldichlorosilane), Bentone 34 (hydrous magnesium aluminum
silicate pigment suspending agent) and clay. Additionally, the
coating compositions of the present invention include wetting
agents such as Triton X-100 (alkylaryl polyether alcohol nonionic
surfactant), Triton CF10 (alkylaryl polyether nonionic surfactant),
Ssilwet 77 (polyalkylene oxide modified dimethylpolysiloxane)
FluorosurfactantFC430 (nonionic liquid fluorosurfactant), Modaflow
(acrylate copolymer) and Witconol (surface wetting agent).
The concentration of the graft initiator i.e.,the silver salt can
vary within a wide range such as 0.001% to 1% by weight of
monomers. In general, the concentration can vary between 0.01% to
0.1% by weight of the monomers.
The concentration of the monomers/prepolymers in the solution can
likewise vary within practically any limits, for example, between
0.1% to 50% of the formulation, though the preferred concentration
is between 0.1% to 20%.
The concentration of the catalyst may vary in the range of 0.1% to
5% of the polymerization solution, though the preferred
concentration is in the range of 0.05% to 1%.
The concentration of fillers used in the formulation vary in the
range of 1 to 30% by weight of the formulation. However, the
preferred concentration may vary in the range of 1 to 20% by
weight.
Preferred examples of the process and coating composition in
accordance with the invention are as follows:
EXAMPLE 1
PARTS BY WEIGHT PART A Epoxy prepolymer Araldite GX 488 N-40 (a
high 100.00 molecular weight bisphenol A epoxy resin solution)
Fluoro polymer polymist F5A 11.00 Polyfluo 200 4.00 Polysilk 14
4.00 Tubular Alumina A1.sub.2 O.sub.3 6.00 Cab-o-sil TS 720 1.00
Cab-o-sil TS 610 1.00 Anticorrosive pigment shieldex 1.00 Mica
C-3000 (micronized muscovite mica having 10.00 an average particle
size of 0.5 microns) Methyl ethyl ketone 76.00 Dowanol PM
(propylene glycolmethyl ether) 15.00 Xylene 20.00 Tungsten
disulfide 4.00 Carbon black monarch 1400 5.00 Molybdenum sulfide
12.00 Super slip 6530 1.00 Monomer silane A 187 2.00 Methyl
methacrylate 0.10 PART B Urethane prepolymer Desmodur N-75
(aliphatic 37.50 polyisocyanate resin based on hexamethylene
diisocyanate and dissolved in n-butyl acetate and xylene) Methyl
ethyl ketone 55.00 Xylene 30.00 Celloslove acetate 15.00 Benzoyl
peroxide 1% in MEK 0.10 Silver perchlorate 0.1% in MEK 0.10 PART C
Catalyst Cycat 4040 (liquid para-toluene sulfonic 0.20 acid
catalyst)
Mixtures (A) (B) and (C) were separately prepared. Mixture (A)
except for silane A 187 and methyl methacrylate was mixed in a
pebble mill for 48 hours. The contents were filtered and the
monomer A187 and methyl methacrylate were added to the (A)
admixture in the ratio indicated and mixed until uniform. Mixture
(B) ingredients were added in the ratio and order as given in the
composition and stirred thoroughly with a mixer to uniform
solution. Mixtures (A) (B) and (C) were then added in the
preparation 273:136:0.2 and then mixed for 10-15 seconds.
EXAMPLE 2
Steel crane pieces were prepared by cleaning with toluene followed
by rinsing with methyl ethyl ketone and then the coating solution
was applied by spraying onto the steel crane pieces or by dipping
the pieces into the coating solution. The steel crane piece is
cured at ambient temperatures for 24 hours. The pieces were tested
for abrasion resistance by the qualitative falling sand method
(ASTM method D-986-51). 25 liters of sand was made to fall on the
coated coupon from a height of 4 ft. No chipping or peeling of the
coating was observed. The adhesion was tested by a cross batch
test, which is as follows: 10 parallel cuts, 1/16" apart were made
through the film and 10 similar cuts were made at right angle (90)
and crossing 10 cuts. Apply tape (3M transparent No.710, 3/4" wide)
over area of cuts by pressing down firmly against coating to
eliminate voids and air pockets. Then sharply pulled tape off at
right angle to the place of the surface being treated. No peeling
off or removal of film was observed.
PARTS BY WEIGHT PART A Epoxy prepolymer DER 684 EK40 (high
molecular 200.00 weight bisphenol A based epoxy resin) Fluoro
polymer polymist F5A 22.00 Polysilk 14 (soft wax polymer having a
melting 8.00 point of 205-245.degree. F.) Polyfluo 200 8.00 Tubular
Alumina A1.sub.2 O.sub.3 12.00 Cab-o-sil TS T20 2.00 Cab-o-sil TS
610 2.00 Anticorrosive pigment shieldex 2.00 Mica C-300 20.00
Methyl ethyl ketone 150.00 Dowanol PM 30.00 Xylene 40.00 Tungsten
disulfide 8.00 Carbon black 10.00 Molybdenum sulfide 24.00 Super
slip 6530 2.00 Monomer silane A 187 4.00 Methyl methacrylate 0.50
PART B Urethane prepolymer Desmodur N-100 (aliphatic 56.25
polyisocyanate based on hexamethylene diisocyanate) Methyl ethyl
ketone 110.00 Xylene 78.00 Celloslove acetate 30.00 Benzoyl
peroxide 1% in MEK 0.20 Silver perchlorate 0.1% in MEK 0.02 PART C
Catalyst Cycat 4040 0.40
Mixtures (A) (B) and (C) were prepared separately and mixed as
outlined in Example 1, except the proportions for mixing were
273:137:0.2. The steel piece was coated and cured as in Example
1.
Steel coupons were coated with the formulation of example 2 by
spraying or dipping. The coated samples were subjected to cure at
room temperature (ambient) for 24-36 hours. However, the coated
samples were also cured at 350.degree. F. for 10-15 minutes. The
coated samples were tested for abrasion and adhesion the same way
as indicated in Example 1. The samples were also tested for
corrosion resistance in 5% salt spray chamber maintained at
95.degree. F. The samples were found to pass 500 hours of salt
spray test.
EXAMPLE 3
PARTS BY WEIGHT PART A Epoxy prepolymer Eponol 53 L 32 (high
molecular 125.00 linear copolymer of epichlorohydrin and bisphenol
A) Flouro polymer polymist F5A 11.00 Polyfluo 200 4.00 Polysilk 14
4.00 Tubular Alumina A1.sub.2 O.sub.3 6.00 Cab-o-sil TS 720 1.00
Cab-o-sil TS 610 1.00 Anticorrosive pigment shieldex 1.50 Mica
C-3000 10.00 Methyl ethyl ketone 50.00 Xylene 16.00 Dowanol PM
20.00 Tungsten disulfide 4.00 Carbon black 5.00 Molybdenum sulfide
12.00 Super slip 6530 1.00 Monomer silane A 187 2.00 Methyl
methacrylate 0.20 PART B Urethane prepolymer Desmodur N-75 37.50
Methyl ethyl ketone 55.00 Xylene 30.00 Celloslove acetate 15.00
Benzoyl peroxide 1% solution in MEK 0.10 Silver perchlorate 0.1%
solution in MEK 0.01 PART C Catalyst Cycat 4040 0.20
Mixtures (A) (B) and (C) were prepared separately and mixed as
outlined in Example 1, except the preparations for mixing were
273:137.5:0.2. Steel samples were coated and cured the same way as
indicated in examples 1 and 2. Samples were found to pass 550 hours
of salt spray test.
EXAMPLE 4
PARTS BY WEIGHT PART A Epoxy prepolymer Araldite GZ488 N-40 100.00
Flouro polymer polymist F5A 8.00 Polyfluo 200 7.00 Polysilk 14 4.00
Tubular Alumina A1.sub.2 O.sub.3 6.00 Cab-o-sil TS 720 1.00
Cab-o-sil TS 610 1.00 Anticorrosive pigment shieldex 1.00 Mica
C-3000 10.00 Methyl ethyl ketone 76.00 Dowanol PM 15.00 Xylene
20.00 Tungsten disulfide 4.00 Carbon black 5.00 Molybdenum sulfide
12.00 Super slip 6530 1.00 Monomer silane A 187 2.00 Monomer silane
SR-350 0.50 PART B Urethane prepolymer Desmodur N-100 28.12 Methyl
ethyl ketone 55.00 Xylene 40.00 Celloslove acetate 15.00 Benzoyl
peroxide 1% in MEK 0.10 Silver perchlorate 0.1% in MEK 0.01 PART C
Catalyst Cycat 4040 0.20
Mixtures (A) (B) and (C) were prepared separately and mixed as
outlined in Example 1, except the preparations for mixing were 273:
137.5:0.2 and in mixture (A) monomer silane A187 and SR-350 were
withheld in the initial mixing and then added to component (A)
prior to mixing with component (B) and (C). The steel samples were
prepared as well as tested the same way as in examples 1, 2 and 3.
Crane steel parts treated in accordance with the process of this
invention in which wear data (thickness of the coating) is taken at
different time intervals over the period of use is presented in
Table 1. No formal side by side comparison tests were made since
the prior condition using various paint coatings, results in bare
metal contact between the boom and the wear pads very quickly.
Typically a lubricating compound is put on the booms in the wear
pads areas from the start. All prior art coatings wear off so
quickly that they have never made them a subject matter of a test.
As can be seen in Table 1 with this inventive coating non
appreciable thickness reduction occurs over the period of use.
Table 1 more specifically shows the results of 1,500 hrs of normal
operating conditions of a telescopic boom crane, generally
operating at approximately 5,000 lbs per square inch wear pad
loading, with the boom sections moving at a velocity in the range
of 1 foot to 2 feet per second. This chart shows that the
protective coating of the invention provides a superior
pressure/velocity tolerance over other coatings, typically paint
type products, which normally gall during the first extension and
retraction of the boom, and thereafter are worn off and expose
generally bare metal after several extensions and retractions of
the boom.
TABLE 1 FIELD TRIAL - UNIT 5/N 22054 (MODEL 656B) PRCA/NCC Polymer
Coating Formulation No. 11 Recorded Coating Thickness on
Telescoping Boom Date Measured Coating Thickness.sup.1 Operating
Hours.sup.2 6/21/93 1.8-2.4 mil - Avg 2.1 mil 1039 4/29/94 1.4-2.0
mil - Avg 1.7 mil 1537 8/28/94 1.2-2.0 mil - Avg 1.6 mil 2539
.sup.1 Coating film thickness on boom top and bottom plates as
measured by Posi-Test mil gage. .sup.2 Crane operation hour
meter.
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